We have a separate page that
discusses how to use the optional features of the FDL.

Where must one put the license notification?

It is sufficient to put the full license notice in the
“main” file of your document. For example, with
the Emacs Lisp Reference Manual, we have many files
included by elisp.texi. We keep the full notification
in elisp.texi, and in the other files we simply write:

What do I do with scripts that are needed to render my document
properly?

We recommend you release these scripts under the GNU FDL as well. Of
course, if these scripts are generally useful for other tasks, it is a
good idea to release them separately under the GNU GPL.

Is it required for the document to have invariant sections?

No. It is perfectly acceptable for a document to have no invariant
sections.

Should I try to make sure the document has some invariant
sections?

Not particularly. If a section's contents ought to be invariant, make
it invariant.

Should I try to avoid invariant sections?

Not particularly. If a section's contents ought to be invariant, make
it invariant.

When should a section be invariant?

First of all, keep in mind that a section that treats technical
material cannot be invariant. Only a secondary section can
be invariant, and a technical section is not a secondary section.

If the section is text that you're not allowed to modify, such as a
copy of the GNU GPL, then it must be invariant. You can't
give permission to modify it if you don't have permission to modify
it.

(One consequence is that you cannot use preexisting text
which covers technical material if you don't have permission to allow
modification of that text.)

When a section discusses the philosophy of free software, it is a good
idea to make that section invariant. For instance, when we put the
GNU Manifesto in a manual, or when we include a section explaining why
free documentation is important, we make that section
invariant.